1. Field
The present invention relates generally to balun signal transformers. More specifically, the present invention relates to balun signal transformers that have high second harmonic rejection.
2. Related Art
A balun (balanced-to-unbalanced) signal transformer is a passive electronic circuit that functions to convert an unbalanced signal (i.e., unbalanced in relation to ground) into balanced signals (i.e., balanced in relation to ground) and vice versa of converting balanced signals into an unbalanced signal. A signal incoming to an unbalanced port of the balun transformer may be divided between two balanced ports of the balun transformer providing signals which have the same amplitude but phases differing by one hundred and eighty degrees in relation to one another. For example, baluns may be used in transmitting circuits and receiving circuits of wireless or cable communications systems and for construction of balanced amplifiers, mixers, voltage controlled oscillators, and antenna systems.
In manufacturing, process variations occur that may affect circuit performance and result in yield loss. For balun transformers circuit performance involves insertion loss, common mode rejection, and second harmonic suppression. Insertion loss is defined as the amount of signal loss occurring in the balun transformer. Common mode rejection is the phenomenon whereby a signal common to two lines gets cancelled at its destination. Second harmonic suppression is the phenomenon whereby signals at frequencies that are two times the fundamental frequencies are rejected to improve performance. Therefore, there is a need for the balun to have a large tolerance for processing variation so that circuit performance and yield are not diminished.